Cylindrical thermal protection cap

ABSTRACT

A cylindrical thermal protection cap for covering a length of an elongated structural element ( 50 ). The cap has a sandwich-like composite insulation system ( 10, 12, 16, 18, 20 ) which has a thermal conductivity lower or equal to 0.11 W/m.° C. at 800° C. and a thickness lower than 50 millimeters.

FIELD OF THE INVENTION

The present invention concerns an insulation system arrangement for thethermal protection of elongated elements, and notably elongatedstructural elements. For instance the present invention concerns thethermal protection of cylindrical structures including cylindrical loadbearing structures, tensile members and their anchorage components ortensioned cables found in external post-tensioning tendons or staycables including their end anchorages.

Such elongated structural elements, and in particular such tensileelements, typically use high strength material, for example highstrength cold-drawn steel, to allow for the transfer of concentratedforces through lightweight elements having small cross sections, notablyused for the transfer of forces in bridges, buildings, special pressurecontainment structures, retaining walls and other structures builtprimarily of concrete or steel. In many cases these tensile elements arepre-tensioned in order to apply a significant pre-load, also calledpre-stress, to the surrounding structure.

Said invention relates to a cylindrical sheath for the thermalprotection of elongated structural elements, and notably forpost-tensioning tendons, stay cables and the like. Such a sheath forms asleeve to be fitted around a running portion of a cable, a tendon or apipe. More generally, this sheath can serve as thermal protection for alength of any structural elongated element made from high tensile steelor other high tensile strength materials susceptible to thermal damage.Said sheath can further be adapted in shape such as to also provideprotection for zones where the running portion of a cable penetratesthrough members of the surrounding or supported structure. Said sheathcan be combined with a cylindrical cap to protect the end terminationsof such cables.

Said invention also relates to a cylindrical cap for the thermalprotection of end terminations of structural elements, and notably forend anchorages of post-tensioning tendons, stay cables or ground anchorsand the like. Such a cap forms a cover to be installed over ananchorage/pipe, notably an anchorage end or a pipe end. This cap canserve in particular as thermal protection for the end of any structuralelongated element made from high tensile strength steel or other hightensile strength material.

More precisely the present invention concerns the protection againstextreme thermal loading scenarios that result for example fromhydrocarbon fires. Elongated structural elements on many different typesof structures can be exposed to such fire events as a result ofaccidents or wilfully caused, for example vehicle or ship impact orspills with the subsequent burning of fuel, burning of hydrocarbonmaterials used in construction or maintenance operations or otherunplanned events during the lifetime of the structure involvinghydrocarbon materials in a solid, liquid or gas state. Such extremeloading scenarios typically result in temperatures exceeding 600° C.,and in some cases exceeding 1000° C. in confined or unconfinedenvironments with durations which can well exceed 30 minutes, andsometimes in excess of 60 or even 90 minutes.

End anchorages of such structural elongated elements conventionally relyon mechanical anchorage by direct bearing or friction or bonding betweendifferent materials to secure highly stressed elements at their end tothe surrounding structure. These end anchorages can either be directlyexposed to a fire event or can experience excessive heating when a fireevent occurs close to the running length of the cable and the cable actssubsequently as a heat conductor.

Such end anchorages participate on satisfying general loading scenariosof the structural elements. When subject to elevated temperatures therelaxation percentage of high tensile strength materials typicallyincreases and their strength decreases. Cold-drawn high tensile strengthsteel is particularly affected by this phenomenon as the strength gainachieved by cold forming the steel during its manufacturing is largelyreversed by heating above a critical temperature, consequently resultingin a loss of pre-stressing forces and a general reduction in structuralresistance. Furthermore excessive heating can lead to slippage orfailure of the stressed element in the end anchorage. Surroundingconcrete or other structural or protective layers along a member's spanoften protect(s) the high strength steel from such an undesirableincrease in temperature, reducing the likelihood of extensive thermalrelaxation and strength loss. End anchorage arrangements, as well astensile members external to a structure, however remain susceptible asthe anchorages are typically exposed to the heightened temperaturesduring an extreme thermal event.

Subsequently, high thermal loading on such highly stressed elongatedstructural elements, including their end terminations, increases thelikelihood of steel relaxation, tendon failure or anchorage slippage orfailure occurring, resulting in an overall loss of pre-stressing forceor ultimate resistance. Due to the surrounding concrete and developedbond between the high tensile steel tendons, made of strands and wires,the consequences of thermal loading in conventional post-tensionedcables internal to a concrete or other structure is reduced. Externalcables however, in particular post-tensioning cables external to thestructure or stay cables, remain highly susceptible to thermal loadingdue to being exposed during an external fire event. The risk of steelrelaxation, tendon failure or anchorage slippage as a direct result ofan external fire event is therefore significantly higher for an externalpost-tensioning cable or a stay cable. Due to the concentrated manner inwhich such cables transfer loads and the low level of redundancy, thestructural safety of civil engineering structures containing externalpost-tensioning tendons, cable stays or other exposed cables, such asbridges, beams, girders, cable supported towers or masts or suspendedroof systems can be severely impacted by the loss of a cable in a fireevent.

The running part of elongated structural members such as externalpost-tensioning cables and in particular stay cables is free to moveunder various effects such as changes in longitudinal elongation,variation of cable sag due to changes in axial cable force or changes ofits deformed alignment due to changing lateral loads, such as wind dragforces, or due to vibrations caused by excitation of the cable due towind effects or by excitation through coupling with vibrations of thestructure caused by fluctuating loads or other external effects. As aresult, the geometrical curve which the running part of the cable adoptscan vary and relatively large movements can occur relative to thesurrounding or supported structure and the cable's end anchorage. Thesemovements can remain unrestrained or if considered detrimental to theperformance of the cable (bending at the anchorage, fatigue, damage bymechanical impact between cable and surrounding structure, unacceptablereduction of comfort for the user of the structure) controlled orlimited by the use of guides, stoppers or dampers fitted between therunning part of the cable and the surrounding structure. It is known todampen such relative movements by viscoelastic means or means acting byrubbing or friction. Such damping means are connected to the cable at acertain distance from the end anchorage in order to develop the requireddamping performance.

Given the flexible nature of such cables and the need to accommodatelarge movements, any thermal protection sheath provided for the runninglength of the cable must be able to adopt its shape to the changing sagline of the cable as well as allowing for relatively large localdisplacements at the interface between the thermal protection elementsand the surrounding structure. Furthermore, the self weight of thesheath must remain small compared to the self weight of the cable if itis supported by the cable in order not to excessively increase the cablesag.

Given the need to fit guides, stoppers or dampers to limit the relativemovements between the cable and the surrounding or supported structure,any thermal protection sheath needs to be easy to remove for the purposeof inspection, maintenance and possible replacement of such devicesduring the lifetime of the structure. The sheath must therefore belightweight and modular.

Such stay cables typically support bridge decks, suspended roofstructures or tall masts and towers which are all exposed to horizontalwind loads. The horizontal loads generated by wind drag on the staycables can be a substantial part of the total horizontal loading on thestructure (exceeding in some cases 50% of the total horizontal windload). Hence it is of utmost importance to minimize the wind drag bylimiting the outer diameter of the stay cables and fitting them withaerodynamically optimized surfaces. Any thermal protection sheath fittedto the cable must hence remain small in diameter.

Contrary to stay cables and some other types of external cables whichare unbonded from the structure, the presence of grout encapsulation inbonded post-tensioning tendons tends to reduce the consequences oflocalised thermal loading on the high tensile steel tendon made ofstrands or wires due to the developed bond between the strands/wires andsurrounding concrete. However, the consequences of anchorage movementand relaxation on unbonded tendons tends to be more severe due to anoverall loss of member integrity as the ability to transfer forcesbetween the tendon and concrete through the developed grout bond isremoved.

Such negative effects are always sensitive for maintaining the safety ofcivil engineering structures containing post-tensioning tendons, cablestays or ground anchors, such as bridges, suspended roof systems andretaining walls, with the safety criteria being even more demanding inthe case of post-tensioning cables and post-tensioning end-anchoragepresent in nuclear facilities and containment structures.

DESCRIPTION OF RELATED ART

Many kinds of piping thermal insulation methods and systems are known.However such systems are specifically developed to reduce the exothermicflow from the covered element, whereas said invention is specificallydesigned to protect the covered element from an external thermal loadingsource, such as fire.

Furthermore, the thermal insulating properties of these conventionalinsulation materials do not suffice in the protection of structuralelements during extreme thermal loading scenarios that typically exceedtemperatures of 1000° C. for exposure durations of 30 minutes or more.

Alternatively, surface applied intumescent products form a protectivecoating for structural elements such that when exposed to a fire loadfor a small exposure interval, satisfactory element protection isprovided. However, such methods and materials do not provide extendedprotection as they typically fail to reduce the conduction of thermalenergy into the structural element during extended high temperatureexposure intervals. Furthermore they are susceptible to mechanicaldamage as they cannot be covered by additional protective layers due tothe need to allow their free expansion to achieve the protectivefunction.

WO2007093703 relates to a fire protection device for a stay cable formedby two blankets wrapped around the cable, and overlapping each other.Also, an outer shell is covering the stacked blankets, this outer shellbeing made of high density polyethylene (HDPE). Such a fire protectiondevice is not suitable for a high level thermal protection unless usingan increased thickness of insulating material, which leads to anincreased and undesirable weight and great difficulties in installationespecially in the interface area where the cable penetrates thesupported structure as well as any guides, stoppers or dampers thatmight have to be fitted.

WO2012052796 provides a thermally insulating rigid tube arranged arounda stay cable with a thermally insulating material having a minimumthickness requiring an air channel between the insulating tube and thecable and a significant height difference to achieve heat evacuation byconvection. Such an arrangement is rigid and cannot thereforeaccommodate the flexure which occurs along the running length of thecable under varying cable sag or the large relative displacements at theinterface where the cable penetrates the supported structure duringnormal working conditions. Such an arrangement can only ensure therequired freedom of movement of the cable by providing a very large airgap between the rigid tube and the cable resulting in a significantincrease of cable diameter having an undesirable impact on the visualappearance of the cable, increasing the required lateral clearance toadjacent parts of the structure and increasing the wind drag of thecable.

BRIEF SUMMARY OF THE INVENTION

It is an aim of the present invention to provide a thermal protectionsheath and a thermal protection cap which mitigates or obviates at leastsome of the above-mentioned disadvantages.

According to the invention, this aim is achieved by means of acylindrical thermal protection sheath for covering a length of anelongated structural element, comprising a sandwich-like compositeinsulation system which has a thermal conductivity lower or equal to0.11 W/m.° C. at 800° C. and a thickness lower than 50 millimetres.

Preferably, for a thickness lower than 50 millimetres, saidsandwich-like composite insulation system has a thermal conductivity at800° C. lower than or equal to 0.10 W/m.° C. and preferably lower thanor equal to 0.09 W/m.° C. Such a thermal protection sheath forms a thinmulti-layered composite construction developed for the extreme extendedthermal protection of length of elongated structural elements, such asexternal post-tensioning cables, cable stays, roof suspension elements,steel profiles and pipe ends, and in particular post-tensioning tendonsand cable stay end anchorages.

The invention also relates to a thermal protection device comprising thecylindrical thermal protection sheath and a cylindrical thermalprotection cap which forms an extreme extended thermal protection of endterminations of elongated structural elements.

The invention also relates to an elongated structural device comprisinga tensioned cable (or any other elongated structural element) with arunning part and at least one anchorage part at the end of the cable,and at least one thermal protection sheath as previously described,wherein said cylindrical thermal protection sheath covers a length ofthe running cable extending from the anchorage part.

Optionally, this elongated structural device further comprises an outercover enclosing the thermal protection sheath.

Another aspect of the invention relates to a cylindrical thermalprotection cap with a single sided closed end, said cap comprising acylindrical wall and an end wall, said cylindrical wall defining anopening for the introduction of the end of an elongated element, saidcylindrical wall and said end wall comprising a composite insulationsystem including at least:

-   -   an outer first layer having a protective outer side,    -   a second layer covering the inner side of said outer first        layer, said second layer being a fabric made from filament and        reinforced yarns, and    -   a third layer covering the inner side of the second layer and        comprising a thermal insulation layer essentially made from        fibers,        wherein at least two layers are stitched together.

Such a cylindrical cap forms a thermal insulating protection capcomprising of a multi-layered composite construction developed for theextreme extended thermal protection of end terminations of elongatedstructural elements, such as post-tensioning cables, cable stays, groundanchors, steel profiles and pipe ends, and in particular post-tensioningtendons and cable stay end anchorages.

The present invention comprises a durable outer first layer having aprotective outer side, which is a metallic, metallic-like ornon-metallic outer side, such as an aluminized fabric or any otherreflective layer, for mechanical protection of the compositeconstruction and increased heat reflection of thermal radiation. Thisouter first layer is preferably fixed with inter-layered stitching to aseries of specifically arranged thermal insulating materials. Thethermal insulation materials preferably consist of both semi-rigid andformable materials which enable the composite cap to form a generalcylindrical shape for generic size fabrication.

The second layer and third layer each form a composite insulating layer,are preferably inter-stitched, and are overlapped with respect to eachother in order to provide extensive coverage of the protected system(elongated element such as a tensioned cable end anchorage) and increaseoverall system efficacy. Each composite layer spans the circumference ofthe cylindrical protection cap and consists of various potentialinsulating materials, of low thermal conductivity, in order to provideboth added strength and reduced thermal conduction. For instance, thethird layer comprises numerous thermal insulating materials of both thefibrous and porous types.

Other provisions according to the invention are presented herein afterin relation with some possible embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the descriptionof an embodiment given by way of example and illustrated by the figures,in which:

FIG. 1A shows an isometric view of an embodiment of a section of acylindrical thermal protection sheath according to the invention.

FIG. 1B shows an isometric view of an alternative embodiment of thecylindrical thermal protection sheath of FIG. 1A,

FIGS. 1C and 1D respectively show an end overview and a detail of thelongitudinal joint of the alternative embodiment of FIG. 1B

FIG. 2 is a perspective view of a thermal protection device, with athermal protection sheath according to the invention, mounted on a staycable system of a civil engineering structure.

FIG. 3 is a perspective view of the stay cable system of FIG. 2 with athermal protection device including a thermal protection cap mounted onthe anchorage and a thermal protection sheath according to the inventionmounted on the length of the running portion extending from theanchorage and also covering the interface area between the civilengineering structure and the cable.

FIG. 4 is a longitudinal section of the stay cable system with thethermal protection device of FIG. 3.

FIG. 4A shows the section of the adjacent elements of the third portionof the thermal protection sheath according direction IVA-IVA of FIG. 4.

FIG. 5 and 6 are enlarged partial views of FIG. 4.

FIG. 7 shows an isometric view of an embodiment of a cylindrical thermalprotection cap.

FIG. 8 is a longitudinal sectional view of the cylindrical thermalprotection cap of FIG. 7.

FIG. 9 is a perspective view of a removable closure band used forinstallation of the cylindrical thermal protection cap of FIGS. 7 and 8.

FIG. 10 is a perspective view of a transparent cylindrical thermalprotection cap mounted on a stay cable anchorage.

FIG. 11 is a perspective view of a thermal protection cap mounted on astay cable anchorage, after complete installation.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

As shown on the embodiment of FIG. 1A the thermal protection sheath 1forms a sleeve of tubular shape, open at both ends. Therefore, thetubular thermal protection sheath 1 is formed by a wall 2 consisting oflayers forming a sandwich. These layers form a composite insulationsystem. Preferably, the thickness and the dimensions (including thediameters when the sheath is formed) of the individual layers of thermalinsulation materials are such that there is contact between the adjacentlayers. In such a configuration, the layers are stacked in the sandwichlike structure of the composite insulation system. A large circularopening 3 is therefore formed at both ends of the tubular thermalprotection sheath 1, to allow for the introduction over the element 80to be protected. The sheath 1 has a tubular shape with a section whichcan be circular or non-circular (for instance a shape such as oval,elliptic, rectangular, square, other quadrilateral or more generallyother polygonal shapes).

In another embodiment shown on FIG. 1B the tubular thermal protectionsheath 1 is further fitted with one or several longitudinal joints 4allowing opening of the tubular section and hence retrofitting over analready installed element to be protected. In order to not increase theoverall diameter of the thermal protection system at the longitudinaljoint 4, the materials forming the overlap are preferably staggered,thus resulting in a continuous material thickness around thecircumference of the system. For instance as shown in FIG. 1C and FIG.1D, along the joint 4, and for the two longitudinal edges of the sheath1, which extends in the direction of the cable 50, outer layers 10, 12and 16 form together a first step 4 ₁ and inner layers 18 and 20 formtogether a second step 4 ₂, offset with respect to the first step 4 ₁.The direction of the offset between the first step 4 ₁ and the secondstep 4 ₂ is inversed for the longitudinal edges of the sheath 1, so thatformation of the longitudinal joint 4 is obtained through abutting thesetwo longitudinal edges of the sheath 1 which shape are thereforecomplementary and can fit together with contact.

In the shown embodiment the composite insulation system is composed offive layers, hereinafter mentioned as first layer 10, second layer 12,third layer 16, fourth layer 18 and fifth layer 20, from the outermostlayer to the innermost layer of the composite insulation system.

The first layer 10 is a protective layer formed of metallic,metallic-like or non-metallic material being made preferably of areflecting material such as aluminized reflective fabric. Moregenerally, this first layer 10 has preferably a metallic-like outer facereflecting thermal energy. This first outer layer 10 provides theexternal layering of said composite insulation system and of saidcylindrical thermal protection sheath 1: it forms an outer cover.Preferably, this is a protective outer cover providing protection to therest of the sheath 1, notably against mechanical damages (such asetching or wear) and/or atmospheric exposure (such as ultraviolet raysprotection). To have the shape of a sleeve with two open ends, as forother layers, the first (outer) layer 10 is for instance formed by arectangular piece attached together by stitching 14 to form a cover thatencompasses the entirety of said sheath external area.

This first layer 10, such as an aluminized reflective fabric, serves inan embodiment to reflect thermal radiation, thus reducing thermal energyinput into subsequent internal layers of the composite insulationsystem. This first layer 10 also serves as thermal insulation. Being theexposed layer of the thermal protection sheath 1, the first layer 10 ispreferably durable, water resistant and has a high tear resistance.

Being susceptible to the environment and exposed to handling duringinstallation, it is preferable that the yarn stitching 14 is of a doublestitched weave to provide system robustness. Also as a preferredcomposition of the yarn material of the stitching 14, one can choosestainless steel or other high temperature material such as glass fibreor Kevlar based fibre, or similar high-strength, high temperaturematerials, or any mixture thereof.

In some cases, the first layer 10 can be omitted: this can particularlyoccur when another outer element covers, and therefore protects, thecomposite insulation system. For instance an external protection can beprovided by other means, i.e. for instance an outer pipe (notillustrated in FIGS. 1A and 1B) wrapping the thermal protection sheath1, which outer pipe can be a HDPE pipe or a steel pipe.

The second layer 12 forms the layer below the first layer 10 (or thissecond layer 12 constitutes a first outer layer when there is no layer10). The second layer 12 is covering the inner side surface of the firstlayer 10. This second layer 12 is placed directly against the inner sideof the first layer 10. Preferably, the second layer 12 is bi-axiallyinter-stitched to the first layer 10 with stitching 14. Thereby, thefirst and second layers 10 and 12 form together an outer assembly of thecomposite insulation system and of the tubular protection sheath 1. Moreprecisely, the first layer 10 is formed by the above-mentionedrectangular piece with two ends which overlap at the circumferenceinterface and are stitched. Therefore the first layer 10 is individuallystitched with stitching 14. Also, the second layer 12 has a layoutanalogous to that of the first layer 10, the circumferential position ofthe overlapping ends of the rectangular piece for the second layer 12being staggered with respect to the circumferential position of theoverlapping ends of the rectangular piece of the first layer 10. Thefirst layer 10 and the second layer 12 are set such that the stitchedconnections are staggered providing continuous cover outside or insidethe respective stitching. The stitching 14 previously mentioned is madewith a thermal resistant thread 15.

According to the invention, the second layer 12 is a fabric consistingof filaments and yarns. These yarns can be reinforced yarns: they serveto reinforce the filaments of the fabric. Therefore, the second layer 12is essentially a primary continuous filament fabric. Preferably, thefabric is a high strength insulation fabric. Also, preferably, thefabric is a high temperature resistant fabric. Consequently, the secondlayer 12 brings cohesion within the composite insulation system.

Preferably, said filaments primarily consist of fabric, preferablymineral fabric, for instance a vermiculite fabric. This second layer 12serves as a high temperature reinforced fabric for added thermalprotection and added overall strength to the thermal protection sheath1. The second layer 12 contributes to the structural integrity of thecomposite insulation system.

Facing the inner side of said second layer 12 is placed the third layer16 made of or mainly formed by a thermal insulation layer which isessentially made from fibers. These fibers are preferably formed bymineral materials. Preferably, said fibers of said third layer 16 aremade from any of the following materials: ceramic, glass or othermineral material. Said thermal insulation layer is therefore preferablyceramic wool, a glass wool or any similar material. This third layer 16preferably forms a thermal wool insulation layer, with fibers which maybe of a mineral or glass composition with a total bulk density relativeto the level of thermal protection required. The third layer 16 iscovering all the inner side surface of the second layer 12. This thirdlayer 16 is placed directly against the inner side of the second layer12.

In an embodiment, the third layer is formed by a fibrous ceramic woolthat enhances thermal insulation properties with a low thermalconductivity.

In a preferred embodiment, said third layer 16 has a thermalconductivity at 200° C. equal to or lower than 0.08 W/m.° C., andpreferably equal to or lower than 0.06 W/m.° C. at 200° C. In apreferred embodiment, said third layer 16 has a thermal conductivity at200° C. comprised between 0.04 and 0.07 W/m° C. Said third layer 16 haspreferably a thermal conductivity at 400° C. equal to or lower than 0.15W/m.° C. at 400° C., and preferably equal to or lower than 0.1 W/m° C.In a preferred embodiment, said third layer 16 has a thermalconductivity at 400° C. comprised between 0.05 and 0.15 W/m° C. Saidthird layer 16 has preferably a thermal conductivity at 800° C. equal toor lower than 0.3 W/m, and preferably equal to or lower than 0.2 W/m.°C. In a preferred embodiment, said third layer 16 has a thermalconductivity at 800° C. comprised between 0.15 and 0.3 W/m° C. Saidthird layer 16 has preferably a thermal conductivity at 1000° C. equalto or lower than 0.5 W/m. ° C., and preferably equal to or lower than0.3 W/m.° C. In a preferred embodiment, said third layer 16 has athermal conductivity at 1000° C. comprised between 0.2 and 0.5 W/m° C.

In an embodiment, said third layer 16 comprises an envelope definingseparate compartments filled with said fibers. For instance, saidcompartments are cross-stitched pockets. This pillowing of the thirdlayer 16 contributes to durability, and allows the insulation of thisthird layer to remain more rigid as to prevent folding or wrinklingduring handling and installation of the thermal protection sheath 1.

Preferably, the composite insulation system comprises a fourth layer 18covering the inner side of the third layer 16, with a micro-porousthermal insulation material. This micro-porous thermal insulationmaterial, such as micro-porous calcium-silicate material, forms a hightemperature thermal insulation barrier.

Said fourth layer 18 has preferably a thermal conductivity at 400° C.equal to or lower than 0.035 W/m.° C., and preferably equal to or lowerthan 0.03 W/m.° C. In a preferred embodiment, said fourth layer 18 has athermal conductivity at 400° C. comprised between 0.025 and 0.035 W/m.°C. Said fourth layer 18 has preferably a thermal conductivity at 600° C.equal to or lower than 0.05 W/m.° C., and preferably equal to or lowerthan 0.04 W/m.° C. In a preferred embodiment, said fourth layer 18 has athermal conductivity at 600° C. comprised between 0.035 and 0.05 W/m° C.Said fourth layer 18 has preferably a thermal conductivity at 800° C.lower than or equal to 0.1 W/m.° C., and preferably equal to or lowerthan 0.07 W/m.° C. In a preferred embodiment, said fourth layer 18 has athermal conductivity at 800° C. comprised between 0.04 and 0.1 W/m° C.

This fourth layer 18 is placed directly against the inner side of thethird layer 16. The fourth layer 18 is covering all the inner sidesurface of the third layer 16.

In an embodiment, said fourth layer 18 comprises an envelope definingseparate compartments filled with said micro-porous thermal insulationmaterial. For instance, said compartments are cross-stitched pockets ofa predefined size based on the dimensional requirements of the thermalprotection sheath 1.

In an embodiment, said micro-porous thermal insulation materialcomprises a silica and/or calcium silicate and/or alumina silicate.Preferably, said micro-porous thermal insulation material comprisespyrogenic silica.

In an embodiment, said micro-porous thermal insulation materialcomprises particles. Such particles are preferably made of oressentially made of silica and/or calcium silicate and/or alumina.

In an embodiment, said composite insulation system is hydrophobic. In anembodiment, said fourth layer 18 is hydrophobic.

The third layer 16 forms a malleable panel at the interspace between thefourth layer 18 and the second layer 12.

Preferably, said third layer 16 and said fourth layer 18 are attached toeach other, for instance by interlayer stitching 14. Depending on thetotal size of said thermal protection sheath 1, it may be necessary touse multiple panels for both the third layer 16 and fourth layer 18,whereby overlapping of the edges of these panels is required at severallocations on the circumference interface of each respective layer 16 and18. Staggering of over-lap along the circumference achieves an increasedthermal protection efficiency. The manner in which the overlap isachieved should be such that no excess material remains such that atight fitting superposed layering as in FIG. 1 results.

A staggered construction technique is implemented for cross-connectionof the fabric layers to envelope the circumference interface as well asbeing staggered between subsequent layers. Such a method is preferred toeliminate the likelihood of a thermal passage forming between stackedlayers 10, 12, 16, 18 and at the interface of each pair of adjacentlayers among the stacked layers 10, 12, 16, 18.

As shown in FIG. 1, in an embodiment, a fifth layer 20 is used as aninner layer in the composite insulation system. Such a fifth layer 20 isplaced against the inner side of the fourth layer 18. Such a fifth layer20 is a durable layer. Preferably, said fifth layer 20 comprises a glassfabric. Such fifth layer 20 provides necessary protection of said fourthlayer 18 as manufacturing, handling and installation of the sheath canresult in structural layer damage.

In an embodiment the fifth layer 20 forms the interface layer betweenfabric layers forming said composite insulation system and a pipe 80.Preferably, said pipe 80 is made of a thermoplastic material, forexample a polyethylene. In an embodiment, said pipe 80 provides theouter enclosure of a high tensile steel cable 50 for example a staycable, for which it provides the necessary installation space andmechanical protection. The cable 50 can be either a solid element ormade up of a group of parallel or stranded wires or groups of strandsmade of wires helically wound around a core wire. In that case, saidpipe 80 is placed between said running part of the cable 50 and thethermal protection sheath 1 as shown in FIGS. 1A and 1B. In anotherembodiment said pipe 80 is an integral part of the stay cable, forexample by being extruded onto the pre-fabricated stay cable during itsfabrication or with a space between said pipe 80 and the cable 50, suchspace being filled with an injection material, for example grease, waxor cement grout. In another embodiment where it is not necessary toprovide an installation space said pipe 80 can be omitted and the fifthlayer 20 is directly adjacent to the cable 50.

In an embodiment, the composite insulation system of the thermalprotection sheath 1 (or of the thermal protection cap 5 described below)comprises at least four thermal insulating layers with at least onelayer forming an outer layer and comprising a reflective fabric, onelayer comprising a high strength thermal fabric, one layer comprising afibrous wool based thermal insulation layer and one layer comprisingpowder filled flexible pocket panels.

In another embodiment, the composite insulation system of the thermalprotection sheath 1 comprises at least three thermal insulating layerswith at least one layer comprising a high strength thermal fabric, onelayer comprising a fibrous wool based thermal insulation layer and onelayer comprising powder filled flexible pocket panels.

Such a thermal protection sheath 1 has been tested according to the ISO834 (1975) “Fire Resistance Tests-Elements of Building Construction”.The ISO 834:1975 standard establishes the resistance of buildingcomponents subjected to standard thermal loading conditions. A thermalprotection device according to the present invention has been testedafter subsequently being installed over the anchor end of a stressingcable located in a concrete substrate. These tests have been conductedwith success according to the temperature curve shown in ISO 834:1975standard, which reaches an environment temperature of 1050° C., after120 minutes. Also, other more drastic tests have been conducted withsuccess with the thermal protection device including a sheath and a cap,in accordance with the hydrocarbon curve referenced in the EuropeanStandard EN 1991-1-2, section 3.2.3, namely with a temperature reaching1100° C. after 30 minutes.

The cylindrical thermal protection sheath 1, and more generally thecomposite insulation system, also serves for protection against otherthermal source such as environmental impacts: direct sunlight exposure,any change in ambient temperature from other sources than fire.

FIGS. 2 to 6, describe a thermal protection sheath 60 forming a sleevefor the protection of a portion of an elongated structural elementforming a tensioned cable 50, for example a stay cable.

In this instance the sandwich-like composite thermal insulation systemmade from the fire protection layers previously described (optionallythe first layer 10, the second layer 12, the third layer 14, the fourthlayer 16 and optionally the fifth layer 18) protects in a preferredembodiment critical elements of a stay cable in the area where theymight become exposed to a fire event. Using a thermal protection sheath60 formed with said sandwich-like composite thermal insulation system,one can obtain a suitable thermal protection of parts of a tensionedcable 50, including guide pipe 55, guide system 70, deviator or damper72, and other components being part of an anchorage 52 (see FIG. 4 toFIG. 6).

In FIGS. 2 to 5, a thermal protection cap 5 is visible at the left sidewhile it covers an anchorage 52 fixed to a load transfer abutment of thecivil engineering structure, for example a blister or panel 51 of thebridge deck 100, and a thermal protection sheath 60 extends the thermalprotection of the tensioned cable 50 from the other side of the loadtransfer member.

To that end, the thermal protection sheath 60 and the thermal protectioncap 5 are formed by a sandwich-like composite thermal insulation system.Namely, the thermal protection sheath 60 contains possibly the firstlayer 10, second layer 12, third layer 14 and fourth layer 16, aspreviously described in relation with the thermal protection sheath 1 or60, and which are superposed, and the thermal protection sheath 60 wrapsa length of the running portion of the tensioned cable 50 extending fromthe anchorage 52.

In FIG. 2, the tensioned cable 50 is mounted on a bridge deck 100,through a blister or panel 51 forming a portion of the concretesubstrate. The anchorage 52 (tensioned cable end) and the thermalprotection cap 5 extends under the bridge deck 100. The running part ofthe tensioned cable 50 and the sheath 60 extend above the bridge deck100. The cable anchorage 52 might alternatively also be located abovethe bridge deck 100 and connected to it by means of a steel or concreteelement such as the panel 51 and protruding upwards from the bridge deck100: in that situation, end portion of the cable 50, thermal protectionsheath 60 and cap 5 are upwardly offset with respect to their positionin FIG. 2.

In the illustrated and preferred embodiment shown in FIG. 4, the thermalprotection sheath 60 comprises three portions 61, 62, 63. Moreprecisely, said sheath 60 has three portions comprising a firstcylindrical portion 61 with a first diameter for covering the length ofan elongated structural element close to an anchorage 52, a secondportion 62 shaped as a frustum of a cone and extending from the firstcylindrical portion 61 with a reducing diameter, and a third cylindricalportion 63 with a third diameter which is smaller than the firstdiameter. In some cases, any of the three portions 61, 62, and 63 isomitted if the respective area is not exposed to a fire event.

The first portion 61 forms an envelope surrounding the length of thetensioned cable 50 extending from the anchorage 52 and housed inside aguide pipe 55 forming a void inside the structure 51. In an embodimentthe guide pipe is fitted with a flange 55 a (see FIG. 5) to support theweight of portions 62 and 63 and other possible elements of the cableassembly such as guides (such as guide system 70 of FIG. 5) and dampers(such as damper 72 of FIG. 5). The guide pipe 55 is sized such as toallow transverse movement of the cable 50 and the first portion 61 isdimensioned so as to fit over the flange 55 a. To that end, there is acylindrical space 61 a between the inner face of the first portion 61and the outer face of the guide pipe 55. The first portion 61 haspreferably a constant internal diameter. At the end of the first portion61 close to the anchorage 52, the first portion 61 is firmly resting onthe concrete panel 51 (slab or abutment). At the end of the firstportion 61 opposite to the anchorage 52, the first portion 61 forms aninward flange 66 for connection with the second portion 62. An optionalrigid cylindrical outer cover 73, for example made of steel, andpossibly formed by two assembled half-shells, may provide additionalprotection and durability for the first portion 61 (see FIG. 4).

In a preferred embodiment, the composite insulation system forming thefirst portion 61 comprises four layers which are the second layer 12,the third layer 16, the fourth layer 18 and the fifth layer 20 aspreviously described. In that case, preferably, the first portion 61 ispreferably covered by said outer cover 73.

The second portion 62 is an envelope surrounding a section of the cable50 installed with the guide or damping means: the second portion 62 isdimensioned such that it does not impede the guide system 70. This isachieved by providing an annular space 62 a between the inner face ofthe second portion 62 and the outer face of the guide system 70. Thesecond portion has a variable internal diameter increasing from theinternal diameter of the first portion 61 (first diameter) to theinternal diameter of the third portion 63 (third diameter). The guidesystem 70 can have several possible configurations and functions, suchas only bundling the cable 50 and being attached to the cable 50, butfree to move relative to the guide pipe 55 (see FIG. 6), or guiding thecable 50 by being fixed relative to the cable 50 and the guide pipe 55(not shown) or being part of a rigid or semi-rigid guide or a damper 72fixed between the cable and the guide pipe 55 (see FIG. 5). Also anouter rigid shell 64 taking the shape of a frustum of a cone covers thesecond portion 62 to provide durability and protection of the secondportion 62.

In a preferred embodiment, the composite insulation system forming thesecond portion 62 comprises five layers which are the first layer 10,the second layer 12, the third layer 16, the fourth layer 18 and thefifth layer 20 as previously described.

In another preferred embodiment, the composite insulation system formingthe second portion 62 comprises four layers which are the second layer12, the third layer 16, the fourth layer 18 and the fifth layer 20 aspreviously described.

The third portion 63 encloses the length of the running portion of thecable 50 by being placed around the outer pipe 80 of the cable 50 in aclose or tight manner with or without a nominal gap. The diameter of thethird portion wrap is hence such that the inner diameter is the same orslightly larger than the outer diameter of the outer face of the cable50. There is a possible relative movement longitudinal to the cable 50between the third portion 63 and the pipe 80 allowing sliding duringinstallation or maintenance operations and during longitudinaldeformation of the cable 50 under varying axial cable loads. As shown inFIG. 6 the third portion 63 can be formed by multiple successive partsattached together. Actually, this third portion 63 can have a small orlarge length, ranging preferably up to 50 meters, and more preferably upto 20 meters and ranging preferably up to 10 meters, notably about from1 to 10 meters. Important lengths are therefore achieved by subsequentconnection of multiple portion units.

In another preferred embodiment, the composite insulation system formingthe third portion 63 comprises four layers which are the second layer12, the third layer 16, the fourth layer 18 and the fifth layer 20 aspreviously described. In that case, preferably, the third portion 63 ispreferably covered by an outer cover 75 (HDPE or steel) possibly formedby a pipe which may provide additional protection and durability for thethird portion 63 (see FIG. 4). This optional rigid cylindrical outercover 75 can also be used in presence of the first layer 10 in thecomposite insulation system forming the third portion 63.

The connection between the first portion 61 and the second portion 62 isachieved through an overlapping splice joint 71 (see FIG. 5). Moreprecisely, the composite insulation system of the first portion 61 andof the second portion 62 both have end portions which are superposed atthe interface. To accommodate relative movements between the cable 50and the guide pipe 55 and therefore also between the first portion 61and the third portion 63, the second portion 62 is fabricated in amanner to allow for flexibility. This is achieved in a preferredembodiment by providing enough geometrical slack in the shape of thesecond portion 62. A similar spliced arrangement is used for theconnection between the second portion 62 and the third portion 63.Preferably, as can be seen in FIGS. 5 and 6, an insulation support board65 is placed at the junction of the second portion 62 and of the thirdportion 63: it supports the outer cover 64 and reduces the passage ofheat from this cover 64 to the cable 50. Preferable the support board 65rests on a spacer tube which in turn rests either on the guide 70 or theguide pipe flange 55 a.

Preferably, the total length of the first portion 61 and second portion62 is equal to or lower to 75% of the total length of the sheath 60.

In a further embodiment at least one portion of the sheath 60, among thefirst portion 61, the second portion 62 and the third portion 63, isformed by two half shells assembled together in a reversible manner.Preferably, both second portion 62 and third portion 63 are formed bytwo half shells. Such a configuration in two parts allows for easyinstallation on pre-existing mounted tensioned cable 50 and alsofacilitates the possibility of control and maintenance of the equipmentof the tensioned cable 50 wrapped within the composite insulationsystem.

Such a configuration, and notably the flexibility of the sandwich-likecomposite insulation system and materials, allows a possible flexuraldeformation of the thermal protection sheath 60, and in particular itsthird portion 63 to follow the variation of sag of the cable 50 due tochanges in axial cable force or changes of its deformed alignment due tochanging lateral loads, such as wind drag forces, or due to vibrationscaused by excitation of the cable due to wind effects or by excitationthrough coupling with vibrations of the structure caused by fluctuatingloads or other external effects. Additional flexural deformation of thesheath 60 can be achieved by providing flexible joints betweenindividual elements of the third portion 63. This is a similar joint asthe spliced arrangement 71 between first and second portions 61, 62 andachieved in a similar manner as described for the longitudinal joint 4with a staggered overlap resulting in a continuous material thicknessalong the length of the system. For instance as shown in FIG. 6, alongthe joint 76, outer layers 10, 12 and 16 form together a first step 76 ₁and inner layers 18 and 20 form together a second step 76 ₂, which isaxially offset with respect to the first step 76 ₁. The direction of theoffset between the first step 76 ₁ and the second step 76 ₂ is inversedfor the transverse edges of the sheath 1, so that formation of the axialjoint 76 is obtained through abutting these two extremities of theadjacent pair of individual elements of the third portion 63 of thesheath 60. The shape of these end edges being therefore complementaryand able to fit together with contact which provides continuousthickness of the wall for the whole third portion 63. Also, it providesa splice connection for adjacent elements of the third portion 63,therefore preventing thermal passage at the interface of two adjacentelements of the third portion 63.

Also, by means of allowing the third portion 63 of the sheath 60 to moverelative to the cable 50 in the longitudinal direction by means ofsliding at the interface the cable 50 remains free to deformlongitudinally under varying axial cable loads. Such load variation canbe caused for example by changes in bridge traffic loading, temperatureand other external loads.

It has been calculated and tested that the composite insulation systemaccording to the invention allows a thermal conductivity lower than orequal to 0.11 W/m.° C. at 800° C. for a thickness lower than 50millimeters, and notably a thickness between 20 and 40 millimeters.

A thermal conductivity at 800° C. equal to or less than 0.10 W/m.° C.,or even equal to or less than 0.09 W/m.° C. can be obtained for thecomposite insulation system according to the invention. In a preferredarrangement, a thermal conductivity at 800° C. ranging from 0.06 W/m.°C. to 0.11 W/m.° C. can be obtained for the composite insulation systemaccording to the invention.Also, these tests and calculations showed that with such a thincomposite insulation system according to the invention, the thermalconductivity performance at other working temperatures reaches also verygood results. Notably, at 200° C., the composite insulation systemaccording to the invention allows a thermal conductivity lower than orequal to 0.01 W/m.° C., lower than or equal to 0.009 W/m.° C. and evenlower than or equal to 0.0085 W/m.° C., preferably ranging from 0.006W/m.° C. to 0.01 W/m.° C.At 400° C., the composite insulation system according to the inventionallows a thermal conductivity lower than or equal to 0.022 W/m.° C.,lower than or equal to 0.02 W/m.° C. and even lower than or equal to0.018W/m.° C., preferably ranging from 0.011 W/m.° C. to 0.022 W/m.° C.At 600° C., the composite insulation system according to the inventionallows a thermal conductivity lower than or equal to 0.084 W/m.° C.,lower than or equal to 0.08 W/m.° C. and even lower than or equal to0.075 W/m.° C., preferably ranging from 0.045 W/m.° C. to 0.084 W/m.° C.For a higher temperature of 1100° C., the composite insulation systemaccording to the invention allows a thermal conductivity lower than orequal to 0.17 W/m.° C., and even lower than or equal to 0.15 W/m.° C.,preferably ranging from 0.10 W/m.° C. to 0.17 W/m.° C.

Also, by means of the previously described sandwich-like compositeinsulation system and the materials used, the sheath 1 or 60 has amaximum weight W_(max) per length unit given by:

W _(max) =K×D[kG]/[m2]

with D the smallest inner diameter of said sheath 60 (in m), W_(max) inkg/m and Factor K between 20 to 30, preferably between 22 to 27, andwhich can be 25. When the sheath 60 is formed in three portions 61, 62and 63 as described above and the third portion 63 has the thirddiameter which is the smallest diameter, D corresponds also sensibly tothe outer diameter of the cable 50 (see FIG. 6).For the sheath 60, this value for the maximum weight W_(max) per lengthunit concerns the third portion 63 which therefore has a small weight(about 1 Kg/m to 10 Kg per m) which remains small compared to the selfweight of the cable 50 which advantageously not excessively increasesthe cable sag and hence tension in the cable 50 (if it is supported bythe cable).

Any variation of the deformed alignment or sag of the cable 50 willresult in rotations at the reference point P between the running lengthof the cable and elements rigidly connected to the supported orsurrounding civil engineering structure such as the guide pipe 55 or theend of the anchorage 52. The reference point P corresponds for exampleto the fixation point of the strand of the cable 50, which is consideredto be located at the terminal end face of the anchorage 52 on the leftof FIG. 4). Such angular rotations (angle α in FIG. 4) can exceed forexample 10 mrad, or for example 25 mrad and can reach up to 50 mraddepending on the length of the cable and the flexibility of the civilengineering structure. Any angular rotation a translates in a relativedisplacement transverse to the longitudinal direction of the cablebetween the running length of the cable 50 and the supported orsurrounding civil engineering structure in discrete points such as forexample at the exit of the guide pipe 55 adjacent to the second portion62 of the sheath 60 requiring to accommodate large transverse movementsby providing for example geometrical slack in the shape of the secondportion 62.

With that configuration, the sheath 60 can accommodate typical flexureof the running part of the cable 50 as well as transverse movementsresulting from typical angular rotations a close to the anchorage 52between the movable parts attached to the cable 50 and the fixed partsattached to the supported or surrounding civil engineering structure.Also, such flexibility is also advantageous for the cable installation,because it allows movements sufficiently large of the cable 50 equippedwith the sheath 60 to have an easy handling.

Preferably, this flexibility is such that said sheath 60 (or sheath 1)can be bent so as to define an arc of circle having a radius R of about2 m or more Notably, said sheath 60 flexibility is such that the thirdportion 63 can be bent so as to define an arc of circle having a radiusR of about 2 m or more (see FIG. 6).Also, said sheath 60 flexibility is such that when the end of the secondportion 62 close to the anchorage 52 is fixed, said sheath portion 62can accommodate a displacement transverse to the longitudinal directionof the cable 50 equivalent to an angular rotation a of the running partof the cable at the exit of the anchorage of at least 50 mrad, followingthereby the movement of the cable 50 (see FIG. 4).Preferably, said sheath 60 (or sheath 1) can accommodate a transversemovement being equal to D, where D is the internal diameter of thesheath 60 (or of sheath 1), or D is the smallest internal diameter ofthe sheath.

As shown in FIG. 4, the sheath 60 forms a thermal protection device 90which, in terms of flexibility, can be defined as having a fixed part 91(first portion 61 of the sheath), a flexible part 92 for transversemovement (second portion 62 of the sheath 60) and a flexible part 93 forbending.

FIG. 4 shows the end part of the anchorage 52 of the cable 50 located onthe side of the concrete panel 51 opposite to the running part of thecable 50. The end part of the anchorage 52 is fitted with an end cap 53providing mechanical protection and sealing. This end cap 53 iscomprised in the fixed part 91.

In an embodiment, and as shown in FIG. 4, a cylindrical thermalprotection cap 5 is used to also protect the end part of the anchorage52 and its cap 53 against fire or other thermal effects. In the presenceof such a cap 5, the fixed part 91 comprises further this thermalprotection cap 5.

As shown on the embodiment of FIGS. 7 to 11, the cylindrical thermalprotection cap 5 forms a sleeve of circular section, open at one end andclosed at the other end. Therefore, the cylindrical thermal cap 5 isformed by a cylindrical wall 6 and an end wall 7 both having the samesuperposed layers forming a sandwich like wall. These stacked layersform a composite insulation system. A large circular opening 8 istherefore formed at the end of the cylindrical thermal protection cap 5,to allow for introduction over the element to be protected.

In the shown embodiment of the cylindrical thermal protection cap 5, thecomposite insulation system is equivalent to the one described forsheath 60 and composed of five layers, previously mentioned as firstlayer 10, second layer 12, third layer 16, fourth layer 18 and fifthlayer 20, from the outermost layer to the innermost layer of thecomposite insulation system.

In an embodiment the fifth layer 20 forms the interface layer betweenfabric layers forming said composite insulation system and a framestructure 24 with elements 22. Preferably, said frame structure 24 is ametallic frame or a ceramic frame or a combination thereof. Preferably,said frame structure 24 has circular rings placed along the length ofthe thermal protection cap 5 and following the inner circumference ofthe thermal protection cap 5. As an option, said frame structure 24further comprises sections parallel to each other and extending alongthe length of the thermal protection cap 5, as illustrated in FIG. 4.

FIG. 8 shows the cross-sectional elevation of a complete thermalprotection device for the end part of an elongated structural element atinstallation, namely said cylindrical thermal protection cap 5 and aclosure band 28 able to be strapped around the end opening 8 of saidcylindrical thermal protection cap 5.

Preferably, in the thermal protection cap 5, and for installationefficiency, the metallic frame 24 is longer than the cylindrical wall ofthe composite insulation system (layers 10, 12, 16, 18 and 20). In thisway, access is provided to the flat-angle brackets 22 for tools used forthe attachment of the metallic frame 24. For instance the flat-anglebrackets 22 are manufactured with holes to allow for mechanical fixation(for instance with bolts).

In an embodiment, said cylindrical thermal protection cap 5 is used witha closure band 28 able to be strapped around the opening 8 of saidcylindrical thermal protection cap 5. FIG. 9 illustrates a removableband 28 that fills the void at the end of the thermal protection devicepost-installation. More precisely, the space formed between the open endof the sleeve (formed by the thermal composition system) and theextremities of the frame (connection elements 22) is closedpost-installation with the closure band 28. In an embodiment, the thirdlayer 16 and the fifth layer 20 form the composition of the removableband 28. 26 is an attachment means forming a connection detail such thatthe removable band 28 is held in place on the thermal protection cap 5post-installation through tightening around the frame 24. In anembodiment shown in FIG. 3, two ribbon sections 29 are placed at the twoends of the removable band 28 able to be connected together by fixationmeans (loops and hooks, or other means such as Velcro system(trademark)). There is also a metallic band 26 (FIG. 3) used as atightening mechanism to hold the removable band 28 around the thermalprotection cap 5 in place, as a strapping band.

The removal of band 28 allows for ease of access for the fixation of thethermal protection cap 5, as the flat-angle brackets 22 are not coveredby the composite insulation system or any other elements.

Handles 30 are preferably used at the outer surface of the thermalprotection cap 5, over the first layer 10, to facilitate the handling ofthe thermal protection cap 5. Handles are interlayer stitched intolayers 10 and 12 for robustness.

As shown in FIGS. 10 and 11, the thermal protection device for the endpart of an elongated structural element comprises said cylindricalthermal protection cap 5, and preferably comprises further an insulationboard 40 with a machined hole. Said insulation board 40 is able to beplaced against the opening 8 of said cylindrical thermal protection cap5, with the hole facing said opening 8. In such a case, the metallicframe 24 is attached to the insulation board 40. In possibleembodiments, the insulation board 40 is a calcium silicate board. Suchan insulation board 40 is precision machined and is mechanically fixed(for instance bolted) to the protected structure, i.e. the concretepanel 51 from which the anchorage 52 extends towards the right in FIGS.10 and 11.

For installation, the metallic frame 24 with the layers 20, 18 and 16already fixed form a first inner assembly. Then the one-piece coverformed by the first layer 10 and the second layer 12 is engaged aroundthe previously attached first assembly: the cover (first layer 10 andsecond layer 12) forming a standalone sleeve or outer assembly that isslid over the third layer 16. The entire assembly consisting of themetallic frame and layers 20, 18, 16, 12 and 10 is then installed overthe end of the elongated structural element to be protected.

The thermal protection cap 5 can range in sizes depending on therequired dimensions of the application. As an example, the thermalprotection device has an outer diameter between 200 millimetres and 1000millimetres, notably about 500 millimetres, and a length of about 500millimetres to 2000 millimetres or more.

Also, the thermal protection cap 5 can have different shapes dependingon the shape of the anchorage 40 and its end cap 52 to be protected, theavailable space at the location of the anchorage and/or depending on thespecific layers used in the composite insulation system of thecylindrical thermal protection cap. In the FIGS. 1 and 2 the first tofifth layers 10, 12, 14, 16, 18 and 20 have a cylindrical wall with acircular section but other section's shape are possible, such as oval,elliptic, rectangular, square, other quadrilateral or more generallyother polygonal shapes.

Such a configuration allows the use of the thermal protection sheath 60and of the thermal protection cap 5 on newly installed and alreadyexisting civil engineering structures for retrofitting of the equipment.

The thermal protection sheath 60 and the optional thermal protection cap5 form a thermal protection device 90 providing a solution for thehigh-level thermal protection of a length (running part and the endpart) of the tensioned cable 50 (or any other structural elongatedelement) running from the anchorage 52. This thermal protection sheath60 can efficiently protect the portion of the tensioned cable 50 aroundwhich it is wrapped by resisting temperatures of 600° C. or more (up to800° C., 1000° C. and in some cases 1200° C.) for a time period of morethan 30 min, namely up to more than 90 min. Such a high level thermalprotection is required to give sufficient time for the arrival of fireresponse teams before the mechanical resistance of the tensioned cableis reduced to a critical point, for instance on a bridge under trafficwhere a fire led to a traffic jam which delays the arrival of the firefighting means, and moreover, this thermal protection sheath 60 providesa low weight solution allowing for a reduced extra weight on thetensioned cable 50, which limits the additional load exerted on thetensioned cable 50 and the overall construction, and also permits themaintenance to parts of the tensioned cable 50 requiring to becontrolled since the portions of the thermal protection sheath 60 whichneed to be taken off can be manual handled, and moreover this thermalprotection sheath 60 does not hinder the free movement of the cable byits flexibility.

In the present text is therefore presented an elongated structuraldevice comprising an elongated structural element such as a tensionedcable 50 with at least one anchorage part 52 (including possibly twoanchorage parts) at the end(s) of the cable 50, and at least one thermalprotection sheath 60, wherein said cylindrical thermal protection sheath60 covers a length of the cable 50 extending from the anchorage part 52.In a possible embodiment, there is also a cylindrical thermal protectioncap 5 covering said anchorage 52.

Preferably, the elongated structural element is an externalpost-tensioned cable or a stay cable.

In the present text it is therefore presented the use of a cylindricalthermal protection sheath 60 as previously described in a civilengineering structure with elongated structural elements having its endsfixed close to or to one anchorage 52, wherein said thermal protectionsheath 60 wraps a length of said elongated structural elements close toat least said anchorage 52. With such a thermal protection sheath 60, isobtained a civil engineering structure, wherein the said cylindricalprotection sheath 60 is able to accommodate transverse movements at thetransition point between the running length of said elongated structuralelement (such as the cable 50) and elements rigidly connected to thesupported or surrounding civil engineering structure equivalent toangular rotation α at the anchorage 52 (reference point P) up to atleast 50 mrad.

In an alternative embodiment of the cylindrical thermal protection cap5, the composite insulation system includes at least:

-   -   an outer first layer having a protective outer side,    -   a second layer covering the inner side of said outer first        layer, said second layer being a fabric made from filament and        reinforced yarns, and    -   a third layer covering the inner side of the second layer and        comprising a thermal insulation layer essentially made from        fibers,        wherein at least two layers are stitched together.

Preferably, at least said first and second layers are stitched together.Preferably first and second layers are stitched together as a pair. In apreferred embodiment, the stitching between the first and second layersis bi-axially inter-stitched to form a robust outer envelope for thethermal protection cap.

As a variant, the first, second and third layers are all inter-stitched.

According to a preferred embodiment of the cylindrical thermalprotection cap 5, said composite insulation system further comprises afourth layer covering the inner side of the third layer and comprising amicro-porous thermal insulation material.

Such a fourth layer has a low thermal conductivity thus forming a hightemperature thermal insulation barrier, while adding structuralintegrity to the composite insulation system forming the cylindricalthermal protection cap. Preferably, this fourth layer is a flexiblemicro-porous layer. Preferably, this fourth layer comprises particles.

According to a preferred embodiment of the cylindrical thermalprotection cap 5, said composite insulation system further comprises afifth layer covering the inner side of the fourth layer. Preferably,this fifth layer is attached to the fourth layer. Preferably, this fifthlayer comprises a structural layer.

Such a fifth layer forms a durable protection layer, which providesadditional protection to the fourth layer, notably mechanical protectionduring the handling of the cylindrical thermal protection cap.Preferably, the fifth layer is stitched to the fourth layer.

According to a preferred embodiment, said cylindrical thermal protectioncap may further comprises a frame placed within said compositeinsulation system and attached to said composite insulation system.

Preferably, this frame is a metallic frame. Alternatively this frame ismade out of ceramic material or of composite materials. Such a frame isnotably required to stabilize the mechanical integrity of the sandwichforming the composite insulation system, in particular for large sizecaps for which the flexibility of the composite insulation system leadsto an unstable shape for the cap in applications of particularorientations.

With a frame, such as a steel frame, the thermal composite layers of thecomposite insulation system are permanently fixed to the rigid frame,the generic structural fitment providing lasting rigidity. Such a framealso facilitates the installation and fixing of the cylindrical thermalprotection cap onto the elongated element or the end of the elongatedelement to be protected.

The invention also relates to the use of such a thermal protection capfor the thermal protection of an elongated structural element. Such anelongated structural element serves for instance as an element providingthe strength and mechanical load resistance to a civil engineeringstructure. Such a thermal protection cap according to the invention canserve for the thermal protection of the end part of any elongated orcylindrical load bearing structure or any cylindrical bearing memberincluding any tensile member (including a post-tensioning tendons andstay cable) and their anchorages.

In particular, the invention relates to the use of such a thermalprotection cap for thermal protection of the end part of apost-tensioning cable anchorage or of a stay cable anchorage or of aground anchor.

As possible application (not shown), the thermal protection cap 5 cancover an anchor element of a tensioned cable, or more generally anelongated tensile element, which's end part is embedded in a concretestructure. Said elongated tensile element can be for example apre-stressing cable used to apply a pre-compression force to saidconcrete structure in order to control undesirable tensile stressesoccurring otherwise in the concrete structure under the application ofexternal loads or deformation. In one embodiment said concrete structurecan be for example a containment structure with a circular shape in planview used to contain matter exerting a positive internal pressure to thecontainment structure and hence resulting in tensile hoop stresses whichare in turn compensated by applying a pre-compression to the concretestructure by means of an embedded pre-stressing cable. Such acontainment structure being for example a storage tank for liquefiednatural gas or a part of the containment vessel in nuclear power plants.Given the importance of the pre-stressing cables for the overallstructural safety of such containment structures, regular inspections orforce measurements are often carried out requiring the removal of thethermal protection cap. Access to the location of the anchor elements isoften difficult due to their height above ground or confined spaces. Itis hence desirable for such thermal protection caps 5 to be light weightto allow their manual handling. In such cases the thermal protection capis required for example to protect the anchorages against fires causedduring maintenance interventions involving electrical equipment, weldingor other heat sources which can develop quickly very high temperaturesdue to the confined conditions and the possible presence of hydrocarbonsin the form of fuel, greases or other products used during maintenanceinterventions.

In another application (not shown) of the thermal protection cap 5, itcovers an anchor element of a tensioned cable, or more generally anelongated tensile element, which's end part is embedded in soil and in aconcrete element covering a portion of the soil. This arrangement formsa ground anchor. The ground anchor is on one end anchored in the soil orrock, for example by means of mechanical interlocking or bond through acementitious injection, and its anchor element on the opposite end isresting against a concrete structure. This arrangement allows topre-stress the ground anchor against the structure and the movement ofthe structure is hence restrained and controlled by the introducedanchoring force. Due to the consolidation or movement of the soil suchground anchors require regular interventions at the anchor element forthe purpose of inspection or measurement of remaining anchor force. Thethermal protection cap 5 must hence be lightweight in order to allow itsmanual handling during these interventions in locations which aretypically exposed and difficult to access due to their height aboveground. Thermal protection caps 5 are typically required where theanchor elements are located adjacent to roads, railroads, navigationchannels or other traffic routes used by vehicles, ships or trainscarrying large amounts of hydrocarbon in the form of fuel or payload inorder to protect the highly loaded anchor elements against the effectsof accidental or wilfully caused fires.

Also, such a configuration allows the use of the thermal protection cap5 according to the invention on already existing civil engineeringstructures for retrofitting of the equipment.

In the present text it is therefore presented the use of a cylindricalthermal protection cap 5 as previously described in a civil engineeringstructure with elongated structural elements having its ends fixed at ananchorage, wherein said thermal protection cap 5 wraps the end of saidelongated structural elements, forming part of said anchorage.

The cylindrical thermal protection cap 5, and more generally thecomposite insulation system, also serves for protection against otherthermal source such as environmental impacts: direct sunlight exposure,any change in ambient temperature from other sources than fire.

In the present text it is therefore presented a cylindrical fireinsulating cap for the thermal protection of end terminations ofstructural elements, and notably for end anchorages of post-tensioningtendons, stay cables or ground anchors and the like. Such a cap forms acover to be installed over an anchorage/pipe, notably an anchorage endor a pipe end. This cap can serve in particular as thermal protectionfor the end of any structural elongated element made from high tensilesteel or other high tensile material.

REFERENCE NUMBERS USED ON THE FIGURES

-   1 Thermal protection sheath-   2 Wall-   3 Opening-   4 Joint-   4 ₁ First step-   4 ₂ Second step-   5 Cylindrical thermal protection cap-   6 Cylindrical wall-   7 End wall-   8 Opening-   10 Outer first layer (metallic outer face)-   12 Second layer (fabric made from filament and reinforcement yarns)-   14 Stitching-   15 Thermal resistant thread-   16 Third layer (thermal insulation layer with fibers)-   18 Fourth layer (micro-porous thermal insulation material)-   20 Fifth layer (structural layer)-   22 Flat-angle brackets-   24 Frame-   26 Attachment means (Metallic band)-   28 Closure band (Strapping)-   29 Attachment means (ribbon sections)-   30 Handle-   40 Insulation board-   50 Tensioned cable-   51 Concrete panel-   52 Anchorage-   53 End cap-   55 Guide pipe-   55 a Flange-   60 Thermal protection sheath-   61 First portion-   61 a Cylindrical space-   62 Second portion-   62 a Annular space-   63 Third portion-   64 Outer cover-   65 Insulation support board-   66 Inward flange-   70 Guide system-   71 Splice joint-   72 Damper-   73 Outer shell-   75 Outer cover-   76 Joint-   76 ₁ First step-   76 ₂ Second step-   80 Pipe-   90 Thermal protection device-   91 Fixed part-   92 Flexible part for transverse movement-   93 Flexible part for bending-   100 Deck-   P Reference point-   α Angle of rotation of deformed sheath-   R Radius of deformed sheath

1. Cylindrical thermal protection cap for covering the end of anelongated structural element, said cap having a cylindrical wall and aclosed end wall, said cylindrical wall defining an opening configuredfor introduction of the end of said elongated structural element, saidcylindrical wall and said end wall comprising a sandwich-like compositeinsulation system which has a thermal conductivity lower or equal to0.11 W/m.° C. at 800° C. and a thickness lower than 50 millimeters. 2.Cylindrical thermal protection cap according to claim 1, wherein saidcap has a maximum weight W_(max) per length unit given by:W _(max) =K×D with K between 20 to 30, D the smallest inner diameter ofsaid sheath or cap (in m), and W_(max) being in Kg/m. 3-9. (canceled)10. Cylindrical thermal protection cap according to claim 1, whereinsaid composite insulation system comprises at least: a second layerbeing a fabric made from filament and reinforcement yarns, and a thirdlayer covering the inner side of the second layer and comprising athermal insulation layer essentially made from fibers.
 11. Cylindricalthermal protection cap according to claim 10, wherein said compositeinsulation system further comprises an outer first layer having aprotective outer side, said second layer covering the inner side of saidouter first layer.
 12. Cylindrical thermal protection cap according toclaim 11, wherein at least two layers among the first layer, the secondlayer and the third layer are stitched together. 13-14. (canceled) 15.Cylindrical thermal protection cap according to claim 10, wherein saidfibers of said third layer are made from any of the following materials:ceramic, glass or mineral composition.
 16. Cylindrical thermalprotection cap according to claim 10, wherein said composite insulationsystem further comprises a fourth layer covering the inner side of thethird layer and comprising a micro-porous thermal insulation material.17-18. (canceled)
 19. Cylindrical thermal protection sheath capaccording to claim 16, wherein said micro-porous thermal insulationmaterial comprises particles made of-silica and/or calcium silicateand/or alumina. 20-21. (canceled)
 22. Cylindrical thermal protectionsheath or cap according to claim 16, wherein said composite insulationsystem further comprises a fifth layer covering the inner side of thefourth layer, attached to the fourth layer and comprising a structurallayer.
 23. Cylindrical thermal protection sheath or cap according toclaim 22, wherein said fifth layer comprises a glass fabric. 24.(canceled)
 25. Cylindrical thermal protection cap according to claim 1,wherein said thermal protection cap further comprises a frame placedwithin said composite insulation system and attached to said compositeinsulation system.
 26. Cylindrical thermal protection cap according toclaim 25, wherein said composite insulation system comprises at least: asecond layer being a fabric made from filament and reinforcement yarns,a third layer covering the inner side of the second layer and comprisinga thermal insulation layer essentially made from fibers, and a fourthlayer covering the inner side of the third layer and comprising amicro-porous thermal insulation material, and wherein the frame isattached to said fourth layer of said composite insulation system ofsaid thermal protection cap. 27-28. (canceled)
 29. Elongated structuraldevice comprising a tensioned cable with a running part and at least oneanchorage part at the end of the cable, and at least one thermalprotection cap according to claim 1, wherein said cylindrical thermalprotection cap covers from the end of the anchorage part. 30-35.(canceled)
 36. Cylindrical thermal protection cap having a cylindricalwall and a closed end wall, said cylindrical wall defining an openingfor introduction of the end of an elongated element, said cylindricalwall and said end wall comprising a composite insulation systemincluding at least: an outer first layer having a protective outer side,a second layer covering the inner side of said outer first layer, saidsecond layer being a fabric made from filament and reinforcement yarns,and a third layer covering the inner side of the second layer andcomprising a thermal insulation layer essentially made from fibers,wherein at least two layers are stitched together.
 37. Cylindricalthermal protection cap according to claim 36, wherein said fibers ofsaid third layer are made from any of the following materials: ceramic,glass or mineral composition.
 38. Cylindrical thermal protection capaccording to claim 36, wherein said composite insulation system furthercomprises a fourth layer covering the inner side of the third layer andcomprising a micro-porous thermal insulation material.
 39. Cylindricalthermal protection cap according to claim 38, wherein said micro-porousthermal insulation material comprises particles made of silica and/orcalcium silicate and/or alumina.
 40. Cylindrical thermal protection capaccording to claim 36, wherein at least said first and second layers arestitched together
 41. Cylindrical thermal protection cap according toclaim 36, wherein said composite insulation system further comprises afifth layer covering the inner side of the fourth layer, said fifthlayer being attached to the fourth layer and comprising a structurallayer.
 42. Cylindrical thermal protection cap according to claim 41,wherein said fifth layer comprises a glass fabric.
 43. Cylindricalthermal protection cap according to claim 36, wherein it furthercomprises a frame placed within said composite insulation system andattached to said composite insulation system.